Electrical apparatus



D 1950 c. w. SHERWIN ETAL 2,532,575

ELECTRICAL APPARATUS Filed Aug. 1, 1945 W FIG. I

I VOLTAGE SUPPLY l &

TO GRID I8 INVENTORS CHALMERS W. SHERWIN HENRY A. STRAUS Q/iuu.

ATTORNEY.

Patented Dec. 5, 1950 V ELECTRICAL APPARATUS Chalmers W. Sherwin, Belmont, and Henry A. Straus, Brookline, Mass., assignors, by mesne assignments, to the" United States of America as represented by the Secretary of War Application August 1, 1945, Serial No. 608,305

This invention relates in general to electrical circuits and more particularly to those circuits employed in the production of sawtooth shaped electrical waves.

In many applications of electrical circuits, particularly those in which a fluorescent display is formed on the screen of a cathode ray tube, it is necessary to generate a voltage which increases linearly in amplitude for a certain period of time and then returns to a reference level, repeating this cycle of operation at a predetermined repetition rate. A wave of this type is customarily known in the art as a sawtooth wave and the designation of sawtooth as used hereafter will refer to a wave as described above. 7

In certain radio apparatus, such as radio object locating systems, wherein a movable antenna scans a region in space and presents on a cathode ray tube screen a visual indication of objects lying within the sector scanned, a sawtooth shaped wave which is synchronized with the motion of the scanning antenna is applied to the deflecting means of a cathode ray tube. This waveform must vary as linearly as possible and must begin and cease in a predetermined relationship to the motion of the antenna.

Accordingly, it is one object of my invention to provide a sawtooth generating circuit adaptable for use with radio object locating systems. 1

Another object is to provide a circuit for generating a sawtooth shaped wave of variable slope and duration.

Still another object is to provide a circuit for generating a sawtooth shaped wave having a highly linear slope.

These and further objects of the present invention will be apparent to those skilled in the art upon reference to the following specification, claims, and drawings in which:

Fig. 1 shows the connection of the various elements which comprise in combination the present invention; and,

Fig. 2 shows a cam which may be used as a means for initiating and terminating the sawtooth.

Briefly, the invention employs a so-called boot strap sawtooth generating circuit to produce a highly linear sawtooth wave, the slope of which is determined by voltage impressed onto the sawtooth generator from a D.-C. generator which is mechanically connected to the scanning antenna. The duration of the waveform is controlled by a mechanical or electrical switch which is synchronized with rotation of the scanning antenna. The sawtooth generat- "3 Claims." (01'. 250-36) ing circuit per se employed is not represented or claimed as being novel with this invention, being known in the prior art. An example of this type of circuit may be found in the application of Byron L. Havens, filed May 16, 1944, Serial No. 535,852, entitled Radio Echo System For Plotting Collision Course.

Referring now to Fig. l, a movable antenna 5 is mechanically coupled to a driving motor 8 which in turn is coupled to a D.-C. generator I. The output voltage of generator 1 may be filtered by a suitable network 8 to remove fluctuations. The voltage is then applied to anode ll) of diode II, cathode I2 of which is connected through resistor I3 and capacitor M to a point of reference, or ground, potential. Switch 29-30 is connected across capacitor M in such a fashion that when it is closed the capacitor is short circuited. The juncture point of resistor I3 and capacitor I4 is connected to grid N3 of vacuum tube I9, cathode 20 of which is connected through load resistor 2| to ground. Anode 23 is connected directly to a suitable source of positive voltage. Outputterminai 24 is connected to cathode 20 and feedback from output terminal 24 to the high side of resistor I3 is provided by capacitor 25. Cam 2'! is shown connected in the mechanical coupling. path between antenna 5 and motor 6 to provide switching action of switch 2930.

When the invention is in operation, motor 6 drives antenna 5 in its scanning pattern and in addition turns generator 1. Motor 6 may be of the variable speed type to provide any desirable scanning rate and the voltage output" of generator I will be substantially proportional to the rate of revolution of motor 6. The output of generator I after being filtered is applied through the diode ll across the series combination of resistor I3 and capacitor l4, thereby charging capacitor l4 through a relatively high resistance path. Switch 29-30, which may be mechanical as shown or alternatively an electron discharge device which is rendered conducting at intervals, is normally open. The voltage across capacitor M, which will tend to, rise exponentially at a rate determined by the voltage applied across resistor l3 and capacitor l4 and hence proportional to the rate of revolution of motor 6, is applied to grid 18 of the cathode follower stage. The exponential-voltage rise at the grid I8 is stopped by the regrounding of the capacitor It by the switch 29-30 near the end of the cycle then the switch reopens to repeat the cycle. This peak value of grid Voltages in the sawtooth generator 'circuit-from feeding back into generatorlL A possible method of synchronizing the-pro duction of sawtooth voltages with'the m'otion'of principles of the invention. Hence, all such modifications and adaptations are claimed as may fall fairly within the spirit and scope of the hereinafter appended claims.

What is claimed is:

1. An apparatus for generating a saw-tooth voltage including a resistor and capacitor in series, said capacitor beingshorted by Switching means operable at a variable frequency, and a "source of voltage across said resistor and capaci- :tor-:varying1.as the frequency of switching varies for charging said capacitor through said resistor,

rsaid 'voltage'variationsbeing coordinated with the swithingifrequencycf said switching means and antenna 5 is shown in Fig. 2. 2'1'is .a-d-isc with a notched portion therein, the extent of the notch being determined by the desired proportion of the antenna scanningwzycle over which it is desired that a -s'awtooth voltageshould be genera'ted. In 9a ty'pical instance, "the notch may constitutel a pproximately% of the total periphery of the dis'c. A 'SpI ingfleVe'rlZB is rigidly attachedto a fixed member-atone end,i-the other end riding againstthet'rim of-Zcam Z-l in suc'h afashion that contacts 29 'and 30-- are held'apart except when the free end: of spring 28 passes into'the n'othe'cl portioniof ca mfli. iCarnlZl will normally b'e adjusted so thatroontaots .2 S an dLSU areoperre'd- 'a't the-beginninguofl-acycle of-antenna scanning motion,thereby synchronizingith .pro-

duction of sawtooth :waves withsuch motion.

It will be understood that lpossible methods of switching are notilimited to -aiinechaJnical' means From the; foregoing description? it willz:be see "that the present -inventionrgives afhighlyzflinear sawtooth lswe'ep voltage whichds eat :every ::point synchronized with the 21110131011 of "the removing antenna-regardless of the rate ofcscan whichxis employed. In-additionpthe-amplitude. of the sawtooth voltage will be thasames-regardless.of its slope, thereby obviating the need for any :additional means :forlimiting :the r.3,InO1'II1t -0f: sweep,

voltage-applied to the cathode. ray tube. v, It will: lie-apparenttothose skilled in .-theart that changes: may-be .made inthe-scircuits :describedhereinabove; without departure. from -.the

"35 as shown in Figs. 11 and 2:'but .inay also beeper ,formed by'i'electri'cal :means. :Ffor example, an electron tube which iscbiasedstoicutioffz mayzbe connected-across icapacitor I 4. =W'hen; antenna '5 .moves intoita predetermined," position' thecelectron tube is fired by 'at phctoelectric sdevicetth-us vcausing heavy conduction through the tube which effectively sh'o'rtcircuits capacitor l4; 1

with.the charging'haracteristics of said resistorcapacitor combination to provide a saw-tooth -voltage of substantially constant maximum amplitude across said capacitor at all switching frequencies. I

2. An apparatus as in claim including a multielement "tube .corltrolled by "a grid ='element con nectedfto the junction of said resistor and said capacitor, a cathode element connected through a second resistor to the other sideof said-capaci torpa plate-element connected-to -a--source"of constant "voltage relative to said *other side of said capacitor, a-"second "capacitorconnected 'between said cathode ==and the other *end of said resistor to produceamorelinearsaw tooth voltage variation, "diod-e rectifier means between said other end of said resistor and "said variable VOIta-g source 'tdprevent *feed-back.

3. Air apparatus-as-in"claim 1' including a';gen-* erator producingvoltage proportionakto speed as said source "of vintage an'd'an actuator 1 for said switching means} both drivenby a variable speed motor.

W. 'SHER-WIN.

HENR/Y STRAU'S.

[CITED .Ihe "following -references are'of record in the file of this 'patent:

zUNLETED. STATES -.PA5IEN-.TS-

Number ilarzie 7 Date" 23130918 "Tolson l Sept.20,"l938 '2';22l*,57-9 Gull iksen l Nov. 12, 1940' 2,237,604 -Marique g a 'Apr. 8,1 94 1 2526651 6 Russell ;Dec. 1 6, 1941 23-20,908 '=.Bus-ign-ies June"1,'-1943 2,426,256 Zenor Aug. 26, 1947 U FOREIGN. PATENTS Number Country :Date 151156 l8 -,Great Britain ,-Aug.. 22,1 939 

